vim: fix config and runtime

- Install shared runtime for both full and fuller.
- Switch big to huge as big is just an alias to normal.
- Fix default config path for tiny variant.
- Use upstream default config for both full and fuller.
- Don't mark default config files for backup.
- Don't mix variant files.
- Mark fuller variant config files for backup.
- Update configure arguments and remove deprecated ones.
- Remove deprecated configuration variables.
- Improve descriptions.
- Fix the following error by installing the missing runtime files for
  full and correctly installing the default config for tiny:

  E1187: Failed to source defaults.vim

- Fix the following fuller error by installing the missing directory in
  runtime:

  Error detected while processing /usr/share/vim/vim91/plugin/netrwPlugin.vim:
  line    7:
  E919: Directory not found in 'packpath': "pack/*/opt/netrw"

Fixes: https://github.com/openwrt/packages/issues/20203
Fixes: https://github.com/openwrt/packages/issues/28104
Signed-off-by: George Sapkin <george@sapk.in>

utils/vim/files/defaults.vim

@@ -0,0 +1,12 @@
+set showcmd			" show (partial) command in status line
+set showmatch		" show matching brackets
+set incsearch		" incremental search
+"set autowrite		" automatically save before commands like :next and :make
+set nocompatible	" use vim defaults instead of 100% vi compatibility
+set backspace=indent,eol,start	" more powerful backspacing
+set autoindent		" always set autoindenting on
+set linebreak		" don't wrap words by default
+set textwidth=0		" don't wrap lines by default
+set ruler			" show the cursor position all the time
+
+set backupskip+=/etc/crontabs.*	" fix crontab -e